<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<form method = "get" action = "userServlet">
    用户名：<input type = "text" name = "username"><br/>
    <input type="submit" value = "校验">
</form>

</body>
</html>